1. Field of the Invention
The present invention relates generally to a semiconductor device package, and in particular to a semiconductor device package structure which permits a significant decrease in package parasitic effects such as inductance and crosstalk.
2. Description of the Related Arts
For the assembly of plastic packages, wire bonding techniques are widely used in fabrication of integrated circuits since wiring banding can assure a higher reliability and a lower production cost of semiconductor packages compared with other chip connection techniques such as TAB(tape automated bonding) or Flip-Chip Bonding techniques. Recent advances in integration technology and performance of integrated circuits have achieved increased speed and band-width, and made possible a greater integration density and multi-chip interconnections of integrated devices. For high speed and high density ICs such as micro/millimeter-wave integrated circuit (MMIC) or optoelectronic integrated circuit (OEIC) ICs, wire bonding parasitic effects caused by inductance or interference between bonding wires connecting the device to the lead frame become dominant. Such parasitic effects are more severe at high frequencies, and there are interference, deformation and parasitic effects caused within high frequency components even for low frequency devices.
In particular, for the MMIC using compound semiconductor devices made from, for example GaAs, since the inductance of the lead frame is as small as 1/5-1/10 of the that of bonding wires, the electric property of the bonding wires has a more important role in improving high frequency characteristics of the semiconductor device packages. Further, multiple-bonding techniques in which the wires of the ground I/O pins and bypass I/O pins are interconnected to each other in parallel in order to accomplish dissipation of heat generated from simultaneous application of alternative and direct currents to the bonding wires, as well as to accomplish strong bonding between the wires and the device. However, although the multiple-bonding wires are advantageous over single-bonding wires in the light of greater reduction in the current density and better heat dissipation, provision of multiple bonding wires gives no satisfactory reduction in the impedance level, since the mutual inductance increases as the pitch between bonding wires becomes fine. The unsatisfactory reduction in the impedance level may be attributed by the mutual magnetic coupling of neighboring bonding wires, which is increasing at high frequency and may cause crosstalk and eventually erroneous operation of devices. If the pitch or distance between bonding wires is increased in order to avoid such crosstalk, the integration density becomes lowered. Accordingly, crosstalk of bonding wires of high-frequency and high-density integrated circuits had been believed to be inevitable.
FIG. 1 is a perspective view of double bonding wire modeling system for the electric characterization of the conventional multiple-bonding wire structure. On the assumption that the ground plane (2) is perfectly grounded, a substrate (4) of 400 .mu.m thickness is attached thereonto. The substrate (4) is provided with double-bonding pads (6) for the ball-bonding of the wires (8a) (8b) on its upper surface. Gold wires (8a, 8b) of 25 .mu.m diameter and 2 mm length are bonded to the bonding pads (6) at one end and to the ground plane (2) at the other end by using a ball-bonding machine. The distance between the bonding wires (8a) and (8b) is 200 .mu.m. Voltage sources (V1) and (V2) are connected between the bonding wires (8a), (8b) and the ground plane (2), respectively to measure mutual magnetic coupling of the bonding wires and (8b).
The ground plane may be replaced with imaginary bonding wires, according to image theory. To take into account effects of conductor loss of bonding wires, caused by a radiation effect, the internal resistance calculated by using "phenomenological loss equivalence method" [H. Y. Lee, T. Itoh, "Phenomenological loss equivalence method for planar Quasi-TEM transmission lines with a thin normal conductor or superconductor" IEEE Trans. Microwave Theory and Tech., Vol. 37, No. 12, December 1989] is inputted equivalently into the analytically divided wires [Method of Moments (MoM)[W. L. Stuzman and G. A. Thiel, "Antenna Theory and Design", John Wiley and Sons, Inc., 1981] using the lumped element loading method. The self and mutual inductances (L, M) of bonding wires are calculated from the values of input impedance (Ze) when in-phase voltage (V1=1[V], V2=1[V]) is applied to the individual bonding wires and of input impedance (Zo) and radian frequency (.omega.) when voltage supply having a phase difference of 180 degree (V1=1[V], V2=1[V]) is applied to the individual bonding wires. EQU L=Im (Ze+Zo)/2.omega. (1) EQU M=Im (Ze-Zo)/2.omega. (2)
The relationship between radius (a) of bonding wires, the height (h) from the ground plane to the highest point of bonding wire, distance (d) between individual bonding wires and static mutual inductance (M) is as follows: EQU Static M=0.1ln{1+(2h/d).sup.2 } (3)
Here, the impedance Z of bonding wire is expressed by following matrix equations: ##EQU1## (herein,
the kernels (.psi..sub.m, p, q =.intg.k (S.sub.m -S')ds', and k(s-s')) are represented by the integration of whole wire circumference; and
s' and s are the source and the field points on the wire axis.)
As can be seen from the equations (1), (2) and (4), the self and mutual inductances (L, M) proportionally increase, depending on the frequency due to an increase in the radiation effect at high frequency. The increase in the mutual inductance (M) may cause crosstalk between individual bonding wires, which consequently causes erroneous operation of elements, as can be seen from the following equation (5): EQU Crosstalk [dB]=20 log (M/L) (5)
Of course, the crosstalk may be avoided by increasing the distance (d), since the mutual inductance (M) is inversely proportional to the distance (d), as shown in equation (3). However, an increase in the distance (d) eventually lowers, integration density of the semiconductor device packages.